A cellular radio access network is a collection of cells that each includes at least one base station capable of transmitting and relaying signals to subscribers' wireless devices. A “cell” generally denotes a distinct area of a mobile network that utilizes a particular frequency or range of frequencies for transmission of data. A typical base station is a tower to which are affixed a number of antennas that transmit and receive the data over the particular frequency. Wireless devices, such as cellular or mobile phones, smart phones, camera phones, personal digital assistants (PDAs) and laptop computers, may initiate or otherwise transmit a signal at the designated frequency to the base station to initiate a call or data session and begin transmitting data.
Mobile service provider networks convert cellular signals, e.g., Time Division Multiple Access (TDMA) signals, Orthogonal Frequency-Division Multiplexing (OFDM) signals or Code Division Multiple Access (CDMA) signals, received at a base station from wireless devices into Internet protocol (IP) packets for transmission within packet-based networks. A number of standards have been proposed to facilitate this conversion and transmission of cellular signals to IP packets, such as a general packet radio service (GPRS) standardized by the Global System for Mobile Communications (GSM) Association, an enhancement of UMTS referred to as Long Term Evolution (LTE), mobile IP standardized by the Internet Engineering Task Force (IETF), as well as other standards proposed by the 3rd Generation Partnership Project (3GPP), 3rd Generation Partnership Project 2 (3GPP/2) and the Worldwide Interoperability for Microwave Access (WiMAX) forum.
A typical 3GPP mobile service provider network, or mobile network, includes a core packet-switched network, a transport network, and one or more radio access networks. The core packet-switched network for the mobile network uses a variety of control protocols to authenticate users and establish logical connections, known as bearers, among the many service nodes on a path between a wireless device, attached to one of the radio access networks, and a packet data network (PDN). The service nodes then utilize the bearers, which employ data protocols, to transport subscriber traffic exchanged between the wireless device and the PDN, which may include, for example, the Internet, an enterprise intranet, a layer 3 VPN, and a service provider's private network. Various PDNs provide a variety of packet-based data services to wireless devices to enable the wireless devices to exchange service data with application or other servers of the PDNs.
To provide the packet-based data services, each mobile service provider network allocates network addresses to the wireless devices in accordance with a network address allocation protocol, such as a dynamic host configuration protocol (DHCP). For example, a DHCP server, Radius server or AAA server may dynamically assign a private address to a customer mobile device upon establishing a network connection for the subscriber equipment. These private network addresses are not routable outside the service provider network. Instead, a network address translation (NAT) device translates the private addresses currently used by each wireless device to public network addresses that are routable within a public network, such as the Internet. That is, upon receiving a first outbound packet for a subscriber communication session (flow), the NAT device selects a public network address and binds a private network address of the outbound packet to the public network address. Thereafter, the NAT device translates the private network address to the public network address for outbound packets and reverse translates inbound packets of the subscriber communication session in accordance with the binding. In many environments, the number of publicly available network address is significantly less than the number of private network addresses that must be supported. These environments utilize network address and port translation (NAPT) in which a private address and port are mapped to a specific combination of a public address and port. As such, different private network addresses for different mobile devices may use different port ranges within the same public network address.